Electronic imagers comprising a plurality of semiconductive photosensitive detectors may be classified according to the type of output circuit which amplifies the photodetector signal. Specifically, in one type of imager, the output circuit comprises a plurality of discrete amplifiers, each amplifier being connected to amplify the signal from a corresponding one of the photodetectors. If the detectors are sensitive to infrared radiation, they are all located inside a cool environment such as a double-walled glass container, called a Dewar flask, and connected to discrete amplifiers located outside of the Dewar. Such an arrangement suffers from the disadvantage that it is bulky and has significant capacitance due to the distance between the detector array located in the Dewar and the amplifiers located outside of it.
These disadvantages are overcome in the prior art by forming the detector array over a semiconductive substrate, the substrate also supporting the output circuitry which comprises a charge coupled device. The entire substrate is contained inside the Dewar. Such an imager is commonly known as a charge coupled device imager and suffers from the disadvantage that charge coupled devices are inherently more noisy than the transistorized amplifiers referred to above.
Accordingly, it is an object of this invention to make an imager having the compactness and low capacitance of charge coupled device imagers without their noisy characteristics.